The present invention relates to a breather device for a motorcycle having a water-cooled V-type engine.
In an engine, gas pressurized in the cylinder bore gradually leaks into the crankcase through a gap between the piston and the cylinder bore. This leaked gas is known as blow-by gas. The pressure of the gas in the crankcase fluctuates as the piston slides, and if the crankcase is hermetically sealed, piston movement is inhibited. Therefore, it is necessary to release the blow-by gas and to separate the oil mist mixed in the blow-by gas with a breather device. In recent years, engines have been made to circulate blow-by gas to an air cleaner to be burned again, thereby preventing air pollution.
A breather chamber within a breather device requires a minimum capacity to separate oil mist from the blow-by gas. However, the layout of a motorcycle engine and the desire to reduce the size of the motorcycle engine make it difficult to store a sufficiently-sized breather chamber. Therefore, a separate breather device must be added, which increases the size, the number of components, and the cost of the engine.
The present invention addresses these problems and provides a simple motorcycle breather device that can effectively utilize available space, thereby reducing the size of the engine.
The present invention provides a breather device for a motorcycle having a water-cooled V-type engine. This type of engine has a crankcase which includes a crankshaft that extends in the crankcase in the widthwise direction of the motorcycle, a plurality of front and rear cylinder assemblies that form a V-shaped profile, a clutch at the rear of the crankcase, and a side cover. The clutch and one end of the crankshaft join at a side wall of the crankcase which is covered by the side cover. Inside this side cover, a breather chamber is formed in the space between the portion of the side cover in front of the clutch mechanism and a platelike oil separator. A shaft, such as a pump shaft, that rotates with the crankshaft is placed parallel to and above the crankshaft between the front and rear cylinder assemblies. A cooling-water pump driven by the pump shaft is placed outside the side cover.
An oil pan can be used to store lubricating oil under the crankcase. This oil pan communicates with the breather chamber through an oil return hole on the lower end of the oil separator. When the motorcycle is running, the level of lubricating oil in the oil pan rises above this oil return hole.
A breather entrance can be formed in the oil separator adjacent to a rotary member, such as an idler-shaft driven gear, thereby transferring the blow-by gas to the breather chamber.
The breather chamber can be divided into an upper and a lower segment by an extended portion formed between the side cover and the oil separator, above the oil return hole and below the end of the crankshaft. This division makes maintenance easier.
The extended portion can contain a check valve that allows the lubricating oil to flow only from the upper segment of the breather chamber into the lower segment of the breather chamber, thereby preventing backflow if the motorcycle tilts.
The shaft that drives the valve mechanism, such as the cam-chain idler shaft, can be coaxial to the shaft that drives the cooling-water pump, such as the pump shaft, thereby making the engine more compact.
A pair of sprockets for driving the valve mechanism, such as a pair of cam-chain driving sprockets, can be placed at the ends of the cam-chain idler shaft which is coupled with the pump shaft. The cooling-water pump is placed beside the gear that is coupled to the crankshaft, such as the idler-shaft driven gear, which is beside one of the sprockets for driving the valve mechanism. This increases engine life.
With the configuration described above, the present invention provides a motorcycle breather device in which a breather chamber effectively utilizes the available space in an engine. The resulting engine is more compact, has fewer components, and has a simpler structure.